An autoinjector is a drug delivery device that contains a medical, therapeutic, diagnostic, pharmaceutical or cosmetic compound (drug) before it is administered, and which is used to administer the compound through the skin of the patient via a hollow needle. Autoinjectors may be used by the patient themselves or by a different user, and may be used to administer drugs to animals.
Autoinjectors are typically used because they reduce the amount of training and effort needed by a user compared with that needed for a syringe, by automating either or both processes of inserting the needle into the patient and expelling the drug through the needle. They can also reduce the fear of injection by hiding the needle from the patient and protect the patient from needle stick injuries.
Autoinjectors typically include a housing containing a drug and a plunger that is driven by an automatic mechanism to move the plunger within the housing to eject the drug. The automatic mechanism may also move the needle relative to the housing to insert the needle into a subject. Motive power for the mechanisms may come from one or more springs or other power sources such as compressed gas.
Autoinjectors are used to deliver so-called crisis drugs such as epinephrine, where a patient may need to self-inject the drug while under the severe stress of anaphylactic shock. They are also used to deliver drugs for long-term conditions such as rheumatoid arthritis, where the patient may have limited dexterity.
In both cases it is beneficial for the autoinjector to have a simple and easy user interface in order to maximise the likelihood that the patient is able to operate the autoinjector correctly and receive the drug. It would also be desirable to provide an audible indication to the patient that drug delivery has been successfully completed.
It is also desirable for the autoinjector to be small, reliable and robust, simple to manufacture, secure during transport and before intended use, and suitable for drugs having high viscosity.